hw/arm/virt: KVM: Enable PAuth when supported by the host

Add basic support for Pointer Authentication when running a KVM
guest and that the host supports it, loosely based on the SVE
support.

Although the feature is enabled by default when the host advertises
it, it is possible to disable it by setting the 'pauth=off' CPU
property. The 'pauth' comment is removed from cpu-features.rst,
as it is now common to both TCG and KVM.

Tested on an Apple M1 running 5.16-rc6.

Cc: Eric Auger <eric.auger@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220107150154.2490308-1-maz@kernel.org
[PMM: fixed indentation]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index e790d6c..71c3ca6 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -491,6 +491,12 @@ static int read_sys_reg64(int fd, uint64_t *pret, uint64_t id)
     return ioctl(fd, KVM_GET_ONE_REG, &idreg);
 }
 
+static bool kvm_arm_pauth_supported(void)
+{
+    return (kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
+            kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_GENERIC));
+}
+
 bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
 {
     /* Identify the feature bits corresponding to the host CPU, and
@@ -521,6 +527,17 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
      */
     struct kvm_vcpu_init init = { .target = -1, };
 
+    /*
+     * Ask for Pointer Authentication if supported. We can't play the
+     * SVE trick of synthesising the ID reg as KVM won't tell us
+     * whether we have the architected or IMPDEF version of PAuth, so
+     * we have to use the actual ID regs.
+     */
+    if (kvm_arm_pauth_supported()) {
+        init.features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
+                             1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
+    }
+
     if (!kvm_arm_create_scratch_host_vcpu(cpus_to_try, fdarray, &init)) {
         return false;
     }
@@ -865,6 +882,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
         assert(kvm_arm_sve_supported());
         cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SVE;
     }
+    if (cpu_isar_feature(aa64_pauth, cpu)) {
+        cpu->kvm_init_features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
+                                      1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
+    }
 
     /* Do KVM_ARM_VCPU_INIT ioctl */
     ret = kvm_arm_vcpu_init(cs);